feat: add support for slave start TCP connect as client

README.md

@@ -50,6 +50,18 @@ handler.Logger = log.New(os.Stdout, "test: ", log.LstdFlags)
 err := handler.Connect()
 defer handler.Close()
 
+client := modbus.NewClient(handler)
+results, err := client.ReadDiscreteInputs(15, 2)
+results, err = client.WriteMultipleRegisters(1, 2, []byte{0, 3, 0, 4})
+results, err = client.WriteMultipleCoils(5, 10, []byte{4, 3})
+
+// Modbus TCP slave start TCP connect as client
+listener, err := net.Listen("tcp", "MasterIP:Port")
+conn, err := listener.Accept()
+handler := modbus.NewTCPClientHandler("")
+handler.UseConnect(conn) // listen conn from slave
+defer handler.Close()
+
 client := modbus.NewClient(handler)
 results, err := client.ReadDiscreteInputs(15, 2)
 results, err = client.WriteMultipleRegisters(1, 2, []byte{0, 3, 0, 4})

tcpclient.go

@@ -217,6 +217,13 @@ func (mb *tcpTransporter) connect() error {
 	return nil
 }
 
+func (mb *tcpTransporter) UseConnect(conn net.Conn) error {
+	if mb.conn == nil {
+		mb.conn = conn
+	}
+	return nil
+}
+
 func (mb *tcpTransporter) startCloseTimer() {
 	if mb.IdleTimeout <= 0 {
 		return